Moisture control in sealed electronic packages

A number of issues associated with controlling the internal moisture content of sealed packages are examined. The basic strategy for maintaining a dry internal environment is to incorporate desiccant into the package and it is shown that molecular sieves are well suited to this task. Expressions are developed that predict the moisture content of the package in terms of package design and the external storage environment. Both moisture sealed into the package during assembly and water tht leaks or permeates into the package over its lifetime are accounted for. In this development, the temperature dependences of all quantities of interest are explicitly treated and the actual Langmuir-like adsorption isotherm exhibited by molecular sieves is employed. These equations allow the quantity of desiccant required to meet design objectives to be computed. They also permit one to evaluate the sensitivity of the internal environment to design parameters and storage conditions, and a number of these are discussed. A computer program that has been written to perform these calculations is also described. 32 refs., 33 figs., 4 tabs.